Steam turbine plants of the type mentioned at the beginning are known from the prior art and are used to generate electricity in an electricity grid. Control power is held in readiness in order to maintain the grid frequency in the event of unforeseen disruptions. Every grid operator needs to make available 2% of its temporary generation capacity as a primary control power reserve. This primary control power reserve is typically provided by large power stations with capacities of more than 100 MW. This includes both steam turbine plants and combined gas-and-steam turbine plants.
In order to provide the control power quickly (in under 30 seconds), steam turbine power stations are throttled slightly in normal operation, i.e. steam turbine control valves are incorporated upstream from the steam turbine. When control power then needs to be provided, the throttle valve is opened completely and a power reserve is made available. This primary control power is then maintained for up to 15 minutes.
However, because the maximum efficiency of the steam turbine is achieved only at full power, the power stations are, as a result of the throttling required to provide the power reserve, operated during standard operation with a slightly inferior efficiency in comparison with their maximum possible efficiency.
It is therefore a technical requirement to provide a method for operating a steam turbine plant which enables a power reserve to be provided at the same time as the greatest possible efficiency during standard operation.
DE048596 provides a solution to this, in which it is described that steam is removed from a steam accumulator when there is a sudden increase in load and to quickly increase power, so that it can be fed to a steam turbine which is already in operation. Comparable solutions are known from U.S. Pat. Nos. 2,247,595 A, 1,925,078 A or 3,398,534 A. A corresponding application when a steam turbine is started up is moreover known from EP 0439754 A1, in which steam is removed from a steam store in order to support the steam time with a simultaneously operating waste heat steam generator
However, the prior art is not able to account for the fact that the power output of a steam turbine plant is affected during the loading of the steam store as a result of this loading process. As a result of diverting steam for the steam store, less steam is namely available for the power mode of the steam turbine.